Recently, many studies have been carried out to develop various photocatalyst materials for application to environmental cleaning, odor elimination, dirt elimination, sterilization, and so on. Such a photocatalyst material is designed to utilize a less costly light with a significantly reduced environmental load as an energy source for oxidatively decomposing organic materials and inorganic materials (e.g., nitrogen oxides).
Titanium oxide has been widely known as a photocatalyst which exhibits an activity when exposed to UV-ray. The photocatalyst material has been studied and developed to meet requirements for utilized in interior of house and circumstances hardly exposed to UV-ray. For example, patent reference 1 (Japanese patent publication No. 3601532) discloses a photocatalyst material exhibiting visible-light activity in which oxygen atom sites of titanium oxide crystal are partially substituted with nitrogen atoms.
In the photocatalyst material of patent reference 1, oxygen atom sites of titanium oxide crystal are partially substituted with nitrogen atoms to form a new isolated level in a bandgap of titanium oxide, for having the visible-light activity. When being exposed to photons each having an energy larger than a bandgap energy of titanium oxide, electrons in the isolated level are excited to the conduction band of titanium oxide, leaving holes in the isolated level for exhibiting activation.
However, the isolated level formed in the bandgap of titanium oxide has a small electronic potential, thereby generating poorly oxidizing holes resulting from photoexcitation of electrons by exposure to visible light. Besides, the holes in the isolated level is restricted from freely migrating, exhibiting a poor reactivity to oxidized substrates. Accordingly, the photocatalyst material in the patent reference 1 exhibits a poor oxidative decomposition activity, albeit having visible-light activity.
Tungsten trioxide has a large electronic potential in its valence band (3.1 to 3.2 V vs. SHE, pH=0), thereby holes generated by photoirradiation is highly oxidative. Tungsten trioxide has an electronic potential of 0.3 to 0.5 V (3.1 to 3.2 V vs. SHE, pH=0) at the bottom of its conduction band, thereby being widely known as a photocatalyst material having a visible-light activity.
However, the electronic potential at the bottom of the conduction band is larger than one-electron reduction potential of oxygen (−0.046 V vs. SHE, pH=0), thereby not enabling photoexcited electrons to perform one-electron reduction of oxygen atoms. The photoexcited electrons are recombined to the generate holes, and are utilized to reduce W (VI) of tungsten trioxide to W (V) for exhibiting photochromism, leading to a lowered oxidative decomposition activity. Accordingly, tungsten trioxide exhibits a significantly poor oxidative decomposition activity.
The present invention has been accomplished in view of the above problems, and has an object to provide a photocatalyst material comprising a tungsten trioxide which is activated by irradiation of visible light to exhibit a high oxidative decomposition activity. The present invention also has an object to provide a method for decomposition of organic materials, an interior member, an air-purification device, and an apparatus for preparation of an oxidizing agent by utilizing the high oxidative decomposition activity.